1. Field of the Invention
The present invention relates to a lift-off method of transferring an optical device layer of an optical device wafer, which has the optical device layer stacked on the front face of an epitaxy substrate such as sapphire or SiC (silicon carbide) substrate with a buffer layer provided therebetween, onto a transfer substrate.
2. Description of the Related Art
In the optical device manufacturing process, an optical device wafer is formed by stacking an optical device layer on the front face of an approximately disk-shaped epitaxy substrate such as sapphire or SiC with a buffer layer provided therebetween. The optical device layer is made up of n- and p-type semiconductor layers made of GaN (gallium nitride), INGaP (indium-gallium-phosphorus), or ALGaN (aluminum-gallium nitride). An optical device wafer is formed by forming optical devices such as LEDs (light emitting diodes) or laser diodes in a plurality of areas partitioned by a plurality of streets formed in a grid pattern on the optical device layer. Then, the optical device wafer is divided along the streets, thus manufacturing individual optical devices.
Further, a manufacturing method called lift-off is disclosed in Japanese Patent Laid-Open No. 2004-72052 in order to ensure improved luminance or improved cooling of optical devices. The lift-off method transfers the optical device layer of an optical device wafer onto a transfer substrate such as molybdenum, copper, or silicon substrate. Lift-off is a technique of joining a transfer substrate to the side of the optical device layer of an optical device wafer with a joining metal layer such as AuSn (gold-tin), and irradiating a laser beam at a wavelength (e.g., 257 nm) that penetrates the epitaxy substrate and is absorbed by the buffer layer from the rear side of the epitaxy substrate so as to destroy the buffer layer, after which the epitaxy substrate is peeled off from the optical device layer, thus transferring the optical device layer onto a transfer substrate.